Active and Passive Microenvironment Management Effects on Temperature Profiles and Crop Yield in Ohio Low and High Tunnel Systems

Passive heating by low and high tunnels as well as active root-zone heating systems are proven tools in horticultural production. However, impacts of their individual and combined application on vegetable crop yield, composition and plant microclimates are often under-reported. In two studies at the Ohio Agricultural Research and Development Center in Wooster, OH, we set out to enhance the record of management strategy effects on abiotic environmental conditions and cropping variables in open field and high tunnel settings across a number of years and seasons. In total, temperature data were recorded at  15-min or 30-min intervals over seven years in up to five high tunnels (4 measuring 6.4 x 14.6 m and 1 measuring 9.1 x 24.4 m) covered with a single layer of 6-mil film and managed per the requirements of cool- and warm-season crops. The 4-year study involving the smaller high tunnels involved year-round production of several crops with temporary raised beds and floating row covers. The 3-year study involving the large high tunnel involved the spring and fall production of lettuce in raised beds which were either covered with a clear 0.8-mil low tunnel, subsurface heated with cables, covered and subsurface heated or uncovered and unheated. An identical set of plots was established outside near the same high tunnel. Despite significant variability in temperature and light data, trends were evident. Temperature and light profiles and crop yield followed management and local conditions. Yield appeared to alternate between periods of light and temperature dependency. Investments in active subsurface heating did not always result in temperatures or yield that exceeded those in plots with passive aerial heating. And, datasets such as the ones developed here are useful in testing hypotheses, developing farmer decision aides and assisting farmers in optimizing microenvironment management.